1. Field of the Invention
The present invention relates to a core-pulling mechanism for pulling a slide core and a threaded-pin core in an injection mold, and also relates to the injection mold with the core-pulling mechanism capable of molding plastic articles with an internal threaded hole and a big cave.
2. The Related Art
A conventional injection mold is convenient for manufacturing complicated plastic articles. As shown in FIG. 8, a parting surface of a plastic article 200 is designated by P, a direction of mold opening is labeled as A-A, and both the directions that the internal threaded hole 210 and the cave 220 open on to are perpendicular to the mold opening direction A-A. In order to mold the plastic article 200, a threaded-pin core and a slide core are needed to mold the internal threaded hole 210 and the cave 220 in a mold cavity of an injection mold. While mold opening, the cores should be pulled out from the mold cavity, so a core-pulling mechanism is needed for pulling the cores out from the mold cavity.
FIG. 9 shows a conventional core-pulling mechanism. A first inclined guiding slot 11a is defined in a first slider 10a to receive a first inclined pin 20a. A second inclined guiding slot 31a is defined in a second slider 30a to receive a second inclined pin 40a. A hinge shaft 50a has a front rectangular prism end 51a passing through a first hole 12a of the first slider 10a and further passing through a sleeve 13a which is connected to the front wall of the first slider 10a. The hinge shaft 50a further has a rear cylinder end 52a passing through a first rotating hole 81a and a second rotating hole 82a of a base 80a so as to rotate therein. A threaded end 61a of a threaded-pin core 60a is inserted into a second hole 32a of the second slider 30a and received in the mold cavity of the injection mold for molding an internal threaded hole. A rear of the threaded-pin core 60a has a flange 62a withstood by the sleeve 13a and a rectangular cavity 63a defined therein to receive the front rectangular prism end 51a of the hinge shaft 50a. 
While the mold opening, the first inclined pin 20a slides out from the first inclined guiding slot 11a and pushes the first slider 10a backward, thus, the sleeve 13a of the first slider 10a and the flange 62a of the threaded-pin core 60a is spaced apart to allow the threaded-pin core 60a to move backward. Then, the hinge shaft 50a is driven to rotate, and the rotation of the hinge shaft 50a drives the threaded-pin core 60a to rotate and move backward until the threaded-pin core 60 is unscrewed out from the molded plastic article. The second inclined pin 40a slides out from the second guiding slot 31a and pushes the second slider 30a backward. Thus, both the threaded-pin core 60a and the second slider 30a are pulled out.
As described in the aforementioned core-pulling mechanism, the hinge shaft 50a rotates in the base 80a without backward movement. A distance S between the front end 51a and the front inner wall of the rectangular cavity 63a should be long enough to provide a space for backward movement of the second slider 30a so as to avoid colliding with the hinge shaft 50a, but the distance S should also be short enough so as to allow the hinge shaft 51a to provide adequate driving force to carry the threaded-pin core 60a to rotate and move backward. Therefore, the distance S decides the moving displacement of the second slider 30a, and the distance S is determined by the angles of the first and second inclined pins 20a, 40a. However, to mold the plastic article 200 as shown in FIG. 8 which has a big cave 220, a slider core for molding the cave 220 is required long enough and needs a long distance travel to be pulled out from the mold cavity. The core-pulling mechanism of the prior art is not qualified to pull the slider core out from the mold cavity with the restriction of the first and second inclined pin 20a, 40a. Additionally, the structures of the first slider 10a and the second slider 30a are so complicated as to result in complicated structures of the injection mold.